Hyperthyroidism is characterized by hyperadrenergic symptoms (i.e., tachycardia, anxiety, and increased metabolic state). Although hyperthyroid patients often complain about an impairment of sleep, no data are available on sleep characteristics and autonomic cardiovascular control during sleep in these patients. We aimed to assess sleep qualitative indices and autonomic cardiovascular regulation during sleep in hyperthyroidism (Hyperthyr) and after treatment. Six subjects with a first diagnosis of Graves’ disease or hyperfunctioning nodule underwent a complete polysomnographic study (PSG) at the time of diagnosis and after the treatment, when they became euthyroid (Euthyr). ECG and respiratory signals were extracted and samples of consecutive 250–300 beats were analyzed using linear spectral and nonlinear entropy analysis of heart rate variability (HRV), during the different sleep stages. Heart rate was decreased and total power increased in Euthyr compared to Hyperthyr, both during wake and sleep; no changes of the sympathovagal balance were observed. Entropy analysis showed that regularity index was reduced in Euthyr compared to Hyperthyr, suggesting changes in the complexity of the cardiovascular control. Periodic leg movements (PLM) were reduced in Euthyr compared to Hyperthyr. In conclusion, hyperthyroidism seems to be associated with an increased sleep fragmentation, due to PLM and an altered cardiac autonomic control. 1. Introduction Hyperthyroidism (Hyperthyr) is a pathological condition characterized by an overproduction of thyroid hormones manifesting with clinical symptoms and signs of an hyperadrenergic activation, such as tachycardia, anxiety, and weight loss. It has been reported that Hyperthyr is associated with an alteration of cardiac autonomic nervous system (ANS) control, namely, a predominant sympathetic modulation associated with a reduced parasympathetic modulation [1–4]; however, conclusive results are still lacking. Sleep is a physiological process essential for life. Physiologically, sleep can be divided into two different stages, non-REM (NREM) and REM sleep. NREM sleep is characterized by the absence of rapid eyes movements and it can be identified into light sleep (N1 and N2) and deep sleep (N3). Interestingly, it has been shown that ANS fluctuates among the different sleep stages: a progressive reduction of sympathetic modulation and an increase of parasympathetic control are described during NREM sleep while, on the opposite, REM sleep is associated with important surges of sympathetic activity [5–9]. The analysis of
References
[1]
M. V. Pitzalis, F. Mastropasqua, F. Massari et al., “Assessment of cardiac vagal activity in patients with hyperthyroidism,” International Journal of Cardiology, vol. 64, no. 2, pp. 145–151, 1998.
[2]
J. Burggraaf, J. H. M. Tulen, S. Lalezari et al., “Sympathovagal imbalance in hyperthyroidism,” The American Journal of Physiology: Endocrinology and Metabolism, vol. 281, no. 1, pp. E190–E195, 2001.
[3]
M. Petretta, D. Bonaduce, L. Spinelli et al., “Cardiovascular haemodynamics and cardiac autonomic control in patients with subclinical and overt hyperthyroidism,” European Journal of Endocrinology, vol. 145, no. 6, pp. 691–696, 2001.
[4]
V. Cacciatori, F. Bellavere, A. Pezzarossa et al., “Power spectral analysis of heart rate in hyperthyroidism,” Journal of Clinical Endocrinology and Metabolism, vol. 81, no. 8, pp. 2828–2835, 1996.
[5]
K. Narkiewicz, N. Montano, C. Cogliati, P. J. H. van de Borne, M. E. Dyken, and V. K. Somers, “Altered cardiovascular variability in obstructive sleep apnea,” Circulation, vol. 98, no. 11, pp. 1071–1077, 1998.
[6]
V. K. Somers, M. E. Dyken, A. L. Mark, and F. M. Abboud, “Sympathetic-nerve activity during sleep in normal subjects,” The New England Journal of Medicine, vol. 328, no. 5, pp. 303–307, 1993.
[7]
F. Iellamo, F. Placidi, M. G. Marciani et al., “Baroreflex buffering of sympathetic activation during sleep: evidence from autonomic assessment of sleep macroarchitecture and microarchitecture,” Hypertension, vol. 43, no. 4, pp. 814–819, 2004.
[8]
P. Cortelli, C. Lombardi, P. Montagna, and G. Parati, “Baroreflex modulation during sleep and in obstructive sleep apnea syndrome,” Autonomic Neuroscience, vol. 169, no. 1, pp. 7–11, 2012.
[9]
I. Berlad, A. Shlitner, S. Ben-Haim, and P. Lavie, “Power spectrum analysis and heart rate variability in stage 4 and REM sleep: evidence for state-specific changes in autonomic dominance,” Journal of Sleep Research, vol. 2, no. 2, pp. 88–90, 1993.
[10]
A. Malliani, M. Pagani, N. Montano, and G. S. Mela, “Sympathovagal balance: a reappraisal,” Circulation, vol. 98, no. 23, pp. 2640–2643, 1998.
[11]
A. Malliani and N. Montano, “Heart rate variability as a clinical tool,” Italian Heart Journal, vol. 3, no. 8, pp. 439–445, 2002.
[12]
N. Montano, A. Porta, C. Cogliati et al., “Heart rate variability explored in the frequency domain: a tool to investigate the link between heart and behavior,” Neuroscience and Biobehavioral Reviews, vol. 33, no. 2, pp. 71–80, 2009.
[13]
A. Monti, C. Medigue, H. Nedelcoux, and P. Escourrou, “Autonomic control of the cardiovascular system during sleep in normal subjects,” European Journal of Applied Physiology, vol. 87, no. 2, pp. 174–181, 2002.
[14]
J. Trinder, J. Kleiman, M. Carrington et al., “Autonomic activity during human sleep as a function of time and sleep stage,” Journal of Sleep Research, vol. 10, no. 4, pp. 253–264, 2001.
[15]
A. Porta, S. Guzzetti, N. Montano et al., “Entropy, entropy rate, and pattern classification as tools to typify complexity in short heart period variability series,” IEEE Transactions on Biomedical Engineering, vol. 48, no. 11, pp. 1282–1291, 2001.
[16]
H. V. Huikuri, T. H. Ma kikallio, and J. Perkiomaki, “Measurement of heart rate variability by methods based on nonlinear dynamics,” Journal of Electrocardiology, vol. 36, supplement 1, pp. 95–99, 2003.
[17]
A. Porta, T. Gnecchi-Ruscone, E. Tobaldini, S. Guzzetti, R. Furlan, and N. Montano, “Progressive decrease of heart period variability entropy-based complexity during graded head-up tilt,” Journal of Applied Physiology, vol. 103, no. 4, pp. 1143–1149, 2007.
[18]
A. Voss, J. Kurths, H. J. Kleiner et al., “The application of methods of non-linear dynamics for the improved and predictive recognition of patients threatened by sudden cardiac death,” Cardiovascular Research, vol. 31, no. 3, pp. 419–433, 1996.
[19]
C. Iber, S. Ancoli-Israel, A. Chesson, and S. F. Quan, The AASM Manual for the Scoring of Sleep and Associated Events, American Academy of Sleep Medicine, Westchester, Ill, USA, 2007.
[20]
A. Rechtschaffen and A. Kales, A Manual of Standardized Terminology: Techniques and Scoring System for Sleep Stages of Human Subjects, UCLA Brain Information Service/Brain Research Institute, Los Angeles, Calif, USA, 1968.
[21]
N. Montano, T. G. Ruscone, A. Porta, F. Lombardi, M. Pagani, and A. Malliani, “Power spectrum analysis of heart rate variability to assess the changes in sympathovagal balance during graded orthostatic tilt,” Circulation, vol. 90, no. 4, pp. 1826–1831, 1994.
[22]
A. U. Viola, E. Tobaldini, S. L. Chellappa, K. R. Casali, A. Porta, and N. Montano, “Short-term complexity of cardiac autonomic control during sleep: REM as a potential risk factor for cardiovascular system in aging,” PLoS ONE, vol. 6, no. 4, Article ID e19002, 2011.
[23]
R. Ferri, M. Zucconi, F. Rundo, K. Spruyt, M. Manconi, and L. Ferini-Strambi, “Heart rate and spectral EEG changes accompanying periodic and non-periodic leg movements during sleep,” Clinical Neurophysiology, vol. 118, no. 2, pp. 438–448, 2007.
[24]
F. Ferrillo, M. Beelke, P. Canovaro et al., “Changes in cerebral and autonomic activity heralding periodic limb movements in sleep,” Sleep Medicine, vol. 5, no. 4, pp. 407–412, 2004.
[25]
G. Merlino and G. L. Gigli, “Sleep-related movement disorders,” Neurological Sciences, vol. 33, no. 3, pp. 491–513, 2011.
